A perfluorinated polyether compound (hereinafter referred to as PFPE) is used as a lubricant, etc. to be applied to the surface of a magnetic recording medium (Non-Patent Document 1).
As such a lubricant, PFPE having two CH2OH groups at its molecular terminals has been commonly used.
Further, the present applicant has proposed the following as PFPE or its composition, which is useful as a lubricant, etc.
(1) PFPE having three CH2OH groups, or PFPE having two CH2OH groups and one CF3 group (Patent Document 1).
(2) An ether composition comprising two types of PFPEs different in the molecular weight (Patent Document 2).
In recent years, along with an increase in the recording density of a magnetic recording medium, narrowing of a space between a recording element and a magnetic recording medium and a trend for high speed of rotation of a magnetic recording medium have been advanced. Accordingly, the application environment of a lubricant to be applied on the surface of a magnetic recording medium has been increasingly severe. Therefore, the lubricant is required to have the following properties.
(i) It has a high fixative to a magnetic recording medium, along with the trend for high speed of the magnetic recording medium.
(ii) It forms a coating having a low friction coefficient surface so that when a recording head contacts magnetic recording media, the impact by the contact is dissipated.
However, PFPE heretofore proposed did not provide sufficient performance to meet such requirements.    Non-Patent Document 1: “Monthly TRIBOLOGY”, 1995, vol. 99, November issue, p. 37-38    Patent Document 1: WO2005/068534    Patent Document 2: WO2007/013412